2010-02-22 - Tung Wai Yip's blog

Refrigerator Madness solution (Facebook programming puzzle)

Refrigerator Madness is the second Facebook programming puzzle I have tried. The problem description is complicated. I won't try to repeat it here but to suggest you to refer to the original facebook page.

To solve this problem it is necessary to see through the smokescreen. Instead of thinking how much Red Bull a Facebook engineer likes to drink, it is easier to map it to a problem known as Two-Sided Matching. A model with intuitive meaning is a marriage matchup between a group of man and woman. Each man has his list of preferred woman and each woman has her list of preferred man. The marriage is considered stable if there are no two people of opposite sex who were not married to each other but would both prefer to be.

For the Refrigerator Madness problem just map the engineer from the upper 50th percentile to "man" and lower 50th percentile to "woman" (or vice versa). The matching condition is equivalent to the stable marriage criteria.

At this point the problem can be solved by applying the Gale-Shapley algorithm. Write the code and it's done!

2010.02.22 [programming] - comments (5)

I don't know python at all. Your link to code, is it real code or psuedo code? If it is real code did it work?

Posted by Madhu at Mon Mar 1 14:59:39 2010

I think your preference computations are incomplete. What happens if a drink is in the list of both Upper Engineer and Lower Engineer but it appears before in Upper Engineer's list than in Lower Engineer's list? In this case you need to add the base value and I don't see that you are doing that.

Posted by Madhu at Mon Mar 1 17:26:07 2010

Yes, it is real code, verified by the Facebook robot.

Regarding the condition you're raise, it is checked below -

elif A[i] not in B[:i]:

You need to know Python's slice operation to understand how it works.

Posted by Wai Yip Tung at Mon Mar 1 19:01:08 2010

Thanks for the response but aren't you just checking for if the drinks are in the same position and if the drink is not in the lower engineer list but what about the drink exists in the both the upper enigneer and lower engineer list but it appear earlier position in the upper engineer list than in the lower engineer list. Please can you show me where is that check done in your code.

Posted by Madhu at Mon Mar 1 20:38:33 2010

B[i] != B[:i]

I hope you have not missed the colon. B[:i] means a sub-list of everything up to index i. So if B is [a,b,c,d], B[:2] is [a,b]. This checking covered 2 cases in the problem description.

Posted by Wai Yip Tung at Tue Mar 2 15:23:04 2010

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